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Register a new userIs there a compact companion orbiting the late O-type binary star HD 164816?
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We present a multi-wavelength (X-ray, $gamma$-ray, optical and radio) study of HD 194816, a late O-type X-ray detected spectroscopic binary. X-ray spectra are analyzed and the X-ray photon arrival times are checked for pulsation. In addition, newly obtained optical spectroscopic monitoring data on HD 164816 are presented. They are complemented by available radio data from several large scale surveys as well as the emph{FERMI} $gamma$-ray data from its emph{Large Area Telescope}. We report the detection of a low energy excess in the X-ray spectrum that can be described by a simple absorbed blackbody model with a temperature of $sim$ 50 eV as well as a 9.78 s pulsation of the X-ray source. The soft X-ray excess, the X-ray pulsation, and the kinematical age would all be consistent with a compact object like a neutron star as companion to HD 164816. The size of the soft X-ray excess emitting area is consistent with a circular region with a radius of about 7 km, typical for neutron stars, while the emission measure of the remaining harder emission is typical for late O-type single or binary stars. If HD 164816 includes a neutron star born in a supernova, this supernova should have been very recent and should have given the system a kick, which is consistent with the observation that the star HD 164816 has a significantly different radial velocity than the cluster mean. In addition we confirm the binarity of HD 164816 itself by obtaining an orbital period of 3.82 d, projected masses $m_1 {rm sin}^{3} i$ = 2.355(69) M$_odot$, $m_2 {rm sin}^{3} i$ = 2.103(62) M$_odot$ apparently seen at low inclination angle, determined from high-resolution optical spectra.
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The X-ray source RX J0648.0-4418 is the only confirmed binary system in which a compact object, most likely a massive white dwarf, accretes from a hot subdwarf companion, the bright sdO star HD 49798. The X-ray emission from this system is characterized by two periodic modulations caused by an eclipse, at the orbital period of 1.55 d, and by the rotation of the compact object with a spin period of 13.2 s. In 2011 we obtained six short XMM-Newton observations centered at orbital phase 0.75, in order to study the system during the eclipse, and spaced at increasingly long time intervals in order to obtain an accurate measure of the spin-period evolution through phase-connected timing. The duration of the eclipse ingress and egress, 500 s, indicates the presence of an X-ray emitting region with dimensions of the order of a few 10^4 km, surrounding the pulsar and probably due to scattering in the companions wind. We derived an upper limit on the spin-period derivative |Pdot|<6x10^-15 s/s, more than two orders of magnitude smaller than the previously available value. Significant X-ray emission is detected also during the 1.2 hours-long eclipse, with a luminosity of about 3x10^30 erg/s. The eclipse spectrum shows prominent emission lines of H- and He-like nitrogen, an overabundant element in HD 49798. These findings support the suggestion that the X-ray emission observed during the eclipse originates in HD 49798 and that the processes responsible for X-ray emission in the stellar winds of massive O stars are also at work in the much weaker winds of hot subdwarfs.
Considering the finite IR behavior of quantum chromodynamics (QCD) running coupling constant in some experiments, we intend to investigate different models presenting running coupling with finite values in the IR region. Using analytic and background perturbation theories, we obtain some equation of states (EoSs) of strange quark matter which satisfy necessary conditions of suitable EoSs. Then we evaluate the properties of strange quark stars in general relativity. Our results for maximum gravitational mass is comparable with the recent LIGO data for the compact binary merger, GW190425.
HD 93129A was classified as the earliest O-type star in the Galaxy (O2~If*) and is considered as the prototype of its spectral class. However, interferometry shows that this object is a binary system, while recent observations even suggest a triple configuration. None of the previous spectral analyses of this object accounted for its multiplicity. With new high-resolution UV and optical spectra, we have the possibility to reanalyze this key object, taking its binary nature into account for the first time. We aim to derive the fundamental parameters and the evolutionary status of HD 93129A, identifying the contributions of both components to the composite spectrum. We analyzed UV and optical observations acquired with the Hubble Space Telescope and ESOs Very Large Telescope. A multiwavelength analysis of the system was performed using the latest version of the Potsdam Wolf-Rayet model atmosphere code. Despite the similar spectral types of the two components, we are able to find signatures from each of the components in the combined spectrum, which allows us to estimate the parameters of both stars. We derive $log (L/L_odot) = 6.15$, $T_{textrm{eff}}=52$ kK, and $log dot{M}=-4.7 [M_odottext{yr}^{-1}]$ for the primary Aa, and $log (L/L_odot)=5.58$, $T_{textrm{eff}}=45$ kK, and $logdot{M}=-5.8 [M_odottext{yr}^{-1}]$ for the secondary Ab. Even when accounting for the binary nature, the primary of HD 93129A is found to be one of the hottest and most luminous O stars in our Galaxy. Based on the theoretical decomposition of the spectra, we assign spectral types O2~If* and O3~III(f*) to components Aa and Ab, respectively. While we achieve a good fit for a wide spectral range, specific spectral features are not fully reproduced. The data are not sufficient to identify contributions from a hypothetical third component in the system.
We present the discovery of WASP-39b, a highly inflated transiting Saturn-mass planet orbiting a late G-type dwarf star with a period of $4.055259 pm 0.000008$,d, Transit Epoch T$_{0}=2455342.9688pm0.0002$,(HJD), of duration $0.1168 pm 0.0008$,d. A combined analysis of the WASP photometry, high-precision follow-up transit photometry, and radial velocities yield a planetary mass of $mpl=0.28pm0.03,mj$ and a radius of $rpl=1.27pm0.04,rj$, resulting in a mean density of $0.14 pm 0.02,rhoj$. The stellar parameters are mass $mstar = 0.93 pm 0.03,msun$, radius $rstar = 0.895pm 0.23,rsun$, and age $9^{+3}_{-4}$,Gyr. Only WASP-17b and WASP-31b have lower densities than WASP-39b, although they are slightly more massive and highly irradiated planets. From our spectral analysis, the metallicity of WASP-39 is measured to be feh,$= -0.12pm0.1$,dex, and we find the planet to have an equilibrium temperature of $1116^{+33}_{-32}$,K,. Both values strengthen the observed empirical correlation between these parameters and the planetary radius for the known transiting Saturn-mass planets.
The emission-line Be star HD 215227 lies within the positional error circle of the newly identified gamma-ray source AGL J2241+4454. We present new blue spectra of the star, and we point out the morphological and variability similarities to other Be binaries. An analysis of the available optical photometry indicates a variation with a period of 60.37 +/- 0.04 d, which may correspond to an orbital modulation of the flux from the disk surrounding the Be star. The distance to the star of 2.6 kpc and its relatively large Galactic latitude suggest that the binary was ejected from the plane by a supernova explosion that created the neutron star or black hole companion. The binary and runaway properties of HD 215227 make it an attractive candidate as the optical counterpart of AGL J2241+4454 and as a new member of the small class of gamma-ray emitting binaries.
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